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Friday, January 3, 2014

No Icicles? Make your Own

Nothing says "winter" like icicles. Those are the frozen spikes that form when dripping water freezes.

If you don't have icicles (yet), and it's cold outside, you can make your own. All you need are:
some coffee cans (or #10 cans)
string
hammer and nail
thumbtack
food coloring

First you need to make something that holds water, but leaks: a can. Start by using the nail to punch three holes around the top rim of each can - evenly spaced. Tie a string through each hole and bring the ends together and tie them in a loop. That's so you can hang your icicle-makers from a tree branch away from sidewalks and driveways.

Then, use the thumbtack to make a hole in the bottom of each can. Make one hole as tiny as possible, and the others of various sizes. On a cold night, cold enough to freeze the water, take your cans outside and fill them half full with water. Add food coloring for tinted icicles. Then hang each icicle-making can on a branch and let it go to work.

In the morning, check on your icicles. Did the size of the hole in the bottom of the can make any difference in the size of your icicles? What happens to them during the day?

One thing you might notice about your icicles is that they all have a "carrot" shape. There's a reason for that, say scientists.As water drips onto an icicle and freezes, it releases heat. The warm air rises up the sides of the icicle and acts like a blanket, or insulator. The insulation is very thin at the tip, and thick at the top. So that's why the tip grows thin and rapidly, and the top grows slowly. Find out more about the math behind icicles here.